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Miter Saw Tolerances

by gauntlet21
posted 11-03-2018 11:20 PM

13 replies so far

View therealSteveN's profile


4672 posts in 1186 days

#1 posted 11-03-2018 11:31 PM

Some have a modicum of adjustment, but even a Kapex if you lock it down, and shake the handle, you will get movement. If you hired a robot to make all of your cuts exactly the same you would maybe get repeatability.

On the rest, and with a human being pulling it down you will get a range. A lot of people using them, don’t want to hear that, but your error is typical.

Fine tools to use for close rough cuts. For fine finish work if thats your tool, cut wide and use a block plane or larger to true and get to final width. A well made sled for a TS is much more likely to get you closer to dead nutz on finish work.

-- Think safe, be safe

View Rick  Dennington's profile

Rick Dennington

6789 posts in 3806 days

#2 posted 11-03-2018 11:39 PM

It’s a sliding saw…You’re trying to over-think this….Just get it adjusted by what the manual says, make a few cuts, and see how close you are to perfect….Once you get it on the money according to the specs, leave it alone….That’s all you can do with any machine that has a blade….!! I have a Delta 12”slider, and it mostly came ready to go right out of the box….A little tweeking, and it was good to go…..!! Just set it, and forget it….!!

-- " There's a better way.....find it"...... Thomas Edison.

View Rich's profile


5157 posts in 1201 days

#3 posted 11-03-2018 11:48 PM

0.0035” per inch isn’t bad. I wouldn’t fuss with it beyond that. That’s assuming you did just one cut. If that’s the fifth cut from a 5 cut test, it’s excellent.

When you’re doing the 5 cut test, what you want to do is make the four cuts, then on the fifth take the strip and measure the difference between ends. You then divide that difference by 4 and then by the length to get the error per inch on each cut. There are different opinions on what constitutes a good result.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Andybb's profile


2406 posts in 1215 days

#4 posted 11-04-2018 12:37 AM

I did the 5 cut test and had a variance of 0.6 degrees on the final cut. I also measured on a single cut, 0.085” of error over 23.75” of length.
- gauntlet21

Since you’re not going to use a 12” ms to make a 24” cut, other than NASA that’s pretty darned good for a sliding spinning shredding piece of sharp metal. Lots of moving tolerance parts in a scms. I’ve never really used anything other than an accurate tri-square on a miter saw. I’d say you’re good. :-)

-- Andy - Seattle USA

View MrRon's profile


5813 posts in 3855 days

#5 posted 11-04-2018 02:07 AM

Any miter saw I have ever checked has side play; some just a little, some too much. The more moving parts in the chain, the more “slop” in the mechanism. Just try not to put any sideways pressure on the handle when pulling/pushing the cutting head. Miter saws, although pretty good for accurate cuts, was originally designed for the construction trade to replace the RAS. Cutting 2×4’s all day doesn’t need a lot of precision.

View SMP's profile


1631 posts in 517 days

#6 posted 11-04-2018 02:51 AM

The stock blade on my dewalt sliding conpound 12” flexes quite a bit. So can depend based on type of wood, how thick, how fast you pull back/chop etc.

View Aj2's profile


2658 posts in 2410 days

#7 posted 11-04-2018 04:04 AM

I agree with SMP a lot depends on the wood type and thickness. Having a good blade will help for getting the most out of a difficult cut.

-- Aj

View ruger's profile


136 posts in 707 days

#8 posted 11-04-2018 10:21 PM

plus 1 with smp. i have a dewalt 780 slider and i make a lot of keepsake boxes with hard maple and other hardwoods. i noticed some of my cuts if laid together on my my unisaw table top after cutting on my miter saw there is a small gap in the cut line, some you can’t see at all.some you can. i’m talking about a 7 inch tall board. if i take that same board and run it through my unisaw the cut is perfect. i.m using 60 tooth blades on both saws. even with a square up against my miter saw and squared up perfect as i can get it i get the same results with my miter saw. going to go with a 1/8 blade on my miter saw on my next blade purchase verse the thin kerf blades they sell everywhere now days. both blades are freud blades. what i do to cut down on the flex is cut the board a fraction longer and go back and shave the end with the last miter saw cut so the blade doesn’t flex. the reason i’m so picky is i’m using a incra ls fence system to make double dovetails on my boxes and if my cuts are not perfect, they show up as small gaps in my dovetails where the joints are glued up. and sanded. and i can not have that at all.

View ruger's profile


136 posts in 707 days

#9 posted 11-04-2018 10:36 PM

View Jared_S's profile


284 posts in 571 days

#10 posted 11-05-2018 12:23 AM

High end trim carpenters use non sliding miter saws most often because there is less play and potential for bad cuts than with a slider. The only time a slider is used is when the cut capacity is needed.

View gauntlet21's profile


69 posts in 822 days

#11 posted 11-05-2018 02:20 PM

Thanks, I was aligning the blade using my Starrett 12” combination square when I thought about a different way to adjust my saw. The manual (as almost all do) mention to adjust your bevel to the bed of the saw and then adjust your blade to the fence or your fence to the blade depending on the model and design. I’ve got the Woodpeckers One Time Tool 26” Precision Woodworking Square (amazing tool) and was using the square to measure the deviation of my cuts. I then remembered that I had seen a YouTube video that mentioned a better tool than even a Starrett combination square for aligning miter guages on the table saw. I figured I could use the same principles in that setup on my miter saw. Here’s a link to the tool: (I am in no way affiliated to any Amazon sales, the manufacturer of the triangle, etc. Just sharing a cheap but great tool for setting up long range cuts).

As I was using the Starrett and algining the blade to the fence, I got out the feeler gauges to see where I was off. I was able to get the Starrett to reject the 0.0015” feeler gauge along the short handle of the 12” version. (I had the 12” rule against the fence and the handle against the blade as the manual instructed). When I went to make a cut, I was getting the error that I mentioned in my first post. I was frustrated because even though there’s flexing in the blade and the sliding components, I was thinking there had to be a better way. I took out my dial indicator and mount to measure the blade for unevenness. Initially, I got 0.0065” which wasn’t scary bad but I thought I would take out the blade and give it a quick cleaning. I also removed the aftermarket bushing and laser guide that I had installed and replaced it with the OEM bushing and my aftermarket blade. The blade is a 12” Amana A.G.E. Thin Kerf 72 Tooth Blade and is about 8 months old. I got the dial indicator to read less than 0.0025” all the way out to the edge of the blade just before the gullets and teeth begin.

With that information, I knew the blade was straight and not the issue. I then used the large Alvin drafting triangle and aligned everything to be square with the miter saw in the down and not extended position. Side note: I aligned the square to the edges of the two carbide teeth (near and far) as the body of the blade cannot be accessed when using such a large straight edge. I then slid the blade toward me to the extended position while listening for the subtle scraping noise of the carbide teeth making contact with the PLASTIC triangle. I am aware that the carbide teeth are precious and losing one would be bad for the blade but its a piece of plastic with no pressure pressing against the tooth. Just a gentle glide. I made minute adjustments until there was contact then entire range of the sliding mechanism on BOTH SIDES of the saw blade.

I then tested the cut and I had a much closer square cut than when I used the combination square. This also incorporated the sliding mechanism. To take things further, I then looking at which side of the cut was short/long and determined if the angle was just over or under 90 degrees. Considering I make almost all of my cuts from the left side of the blade, I made microscopic adjustments to the blade angle until I got a 23.5” x 5” board to reject the 0.0015” feeler gauge. And now, my saw is awesome. I’ve got a shooting board and hand planes but I wanted to know the capabilities of my saw. I asked the question and despite the variables that DO make a sliding miter saw less accurate than a non-sliding one, I’m very pleased with the accuracy of my saw. Cuts from the right side of the saw are just as accurate. I did reach a point where I was plenty pleased with the results but I just kept going to see if consisitent “nearly perfect” cuts could be obtained. I know that cutting boards changes the grain forces, and not to get boggled down by trying to make it perfect but I just needed to see. So I recommend if anyone is having a problem similar to mine, try using a long range square/triangle to magnify the error. I also performed the 5 cut test and that provided consistent and identical results.

Thanks again,


View Rich's profile


5157 posts in 1201 days

#12 posted 11-05-2018 06:10 PM

High end trim carpenters use non sliding miter saws most often because there is less play and potential for bad cuts than with a slider. The only time a slider is used is when the cut capacity is needed.

- Jared_S

Not to mention the fact that they cost about half as much and are far lighter and easier to move to — and around — the job site.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View MrRon's profile


5813 posts in 3855 days

#13 posted 11-05-2018 06:23 PM

A circular saw (any flavor) is a less than perfect way to get a perfectly square cut. There are too many factors that can go against you. First off, the miter saw itself is not perfect. It has side play, bearing tolerances to contend with. The blade itself, especially thin kerf blades have problems. Because of their thinness, the blade will “flutter” due to changes in density of the wood being cut. Feeding the blade too aggressively can cause the blade to drift. Poorly set teeth can cause the blade to pull to one side. In other words, the miter saw is not the saw to use if a perfect cut is to be made. Table saws are much better for that, but again, the blade makes a big difference.

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